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Old 06-16-2018, 11:55 AM
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258 engine rebuild

Haven't gotten block back from machine shop. Started the nasty job of cleaning other parts. It's been about 25 years since I have done an engine forgot how bad cleaning is!
Any suggestions on a cam or should I just stay stock? Mainly will be use for some trail riding and running around back roads

Thanks RN

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Old 06-16-2018, 03:34 PM   #2
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There isn't a lot that you can do to get any more power out of a 258/4.2.
These are low RPM, torquemonsters. You might be able to still find an aftermarket cam or a HO 4.0 cam might work. I'm (slowly) building a 258 that I bought as a core. Besides the .040 bore and a head that's planed just enough to flatten it out I'm going to stay stock.

Folks usually cam an engine to get more RPM out of it. That really doesn't work for the type of driving/wheeling that I do. When building something like an engine and varying from stock, beware of the rule of unintended consequences. IE... A 4.0 HO cam is intended for a FI engine that's timed by the computer. It may or not work well or it might work well with other modifications to the intake/exhaust systems.

You might find an old Edelbrock 4BBL intake manifold that usually comes with a reducer to allow for a 2BBL carb, but why?

Some guys use a 4.2 crank in a 4.0 block but since you already have your block at the machine shop, that probably isn't going to be practical for you.

I'm running a carb because that's what I want.
I think the best overall setup is a Howell FI setup with a HEI distributor.

You state that your use of the Jeep will be some trails and running around back roads.
4:10 gears will give you the biggest bang for your buck for that type of Jeeping.

I'm sure other posters have different opinions. The above is simply mine.
Keep us posted on your progress.

I could type several more paragraphs but that's the meat of it. Don't be shy about asking more questions.

Good Luck, L.M.

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Old 06-16-2018, 03:58 PM   #3
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Get a cam to suit your needs. I will suggest to go with a different head though. The fuel injected 4.0's have larger valves and make considerably more flow, they bolt right on. Do your research as there is one in particular that is superior to the rest.

When I got my YJ it was blowing oil all over the engine bay so sent it to a rebuilder, it came back .040 over. They used soft rubber valve stem seals and it smoked like a cigar till I swapped em for rigids.

Was tired of the vacuum issues and massive nest of tubing so swapped it to a weber carb, did a nutter bypass and still had troubles on inclines so went with a throttle body setup. The throttle body injection is way better than all the other fixes for the carburation troubles. Still had issues on long climbs in the sand and snow though. Just didn't get the horsepower outta that 258.

The final mods that brought the booze to the party was a 4.0 head, HEI distributor and middle of the road cam. Since then it's been non-stop.

Best of luck on your rebuild.
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Old 06-17-2018, 06:25 AM
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Thanks for the input I ordered a HEI distributor last night so today's plan is to remove the ignition module and computer and all the wiring. I would like to remove the vacuum hoses that aren't needed as well. If I have done my research right all I need to leave is vacuum lines for 4wheel drive and vent damper. If that is incorrect please let me know.
I am thinking of putting 4.0 head on but the research I did look like lots of mods needed. Exhaust manifold swap mods to intake if I stay carbed different length push rods.

Thanks RN
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Old 06-19-2018, 05:36 PM
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Got all the computer and ignition mod wiring removed didn't take the computer out looked difficult to get to. Got a call from machine shop my block and crank are done now just have to find time for the 4 hour trip to get them.
They said they bored it 20 over thought that sounded a little strange when I looked on line for rebuild kits they all start at 30 over. I hope they misspoke on the phone will wait until it's home to order the kit.
RN
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Old 07-02-2018, 06:29 PM
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Finally got all my parts the machine shop did bore it to 20 over. Every kit I found started at 30 over so had to by parts individually bummer costed a lot more.
I decided to hang pistons on rods myself saves me a four hour trip. I have never done it before everything I have googled shows people heating rod ends up. I thought that sounded like a bad idea until I found a few videos of machine shops doing it. Has any one done this before? I made a jig last night to position pins correctly but still a little nervous of doing it.
Thanks
RN
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Old 07-06-2018, 11:25 AM   #7
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Quote:
Originally Posted by Nosker View Post
Finally got all my parts the machine shop did bore it to 20 over. Every kit I found started at 30 over so had to by parts individually bummer costed a lot more.
I decided to hang pistons on rods myself saves me a four hour trip. I have never done it before everything I have googled shows people heating rod ends up. I thought that sounded like a bad idea until I found a few videos of machine shops doing it. Has any one done this before? I made a jig last night to position pins correctly but still a little nervous of doing it.
Thanks
RN
I left that to a professional. It looks doable, but you only get one shot. If it cools on you and is out of position it might turn in to a problem.
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Old 06-08-2019, 01:29 AM   #8
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Originally Posted by Timglide View Post


When I got my YJ it was blowing oil all over the engine bay so sent it to a rebuilder, it came back .040 over. They used soft rubber valve stem seals and it smoked like a cigar till I swapped em for rigids.

Hello the engine of my jeep yj (AMC 258) was rebuilt .040 over and a kit comp cams (K68-231-4) and since it smokes and consumes a lot of oil (the compression of the cylinders is good) and I install soft rubber valve stem seals (Part: 504-12).
I would like to know how and with what you have solved this consumption of oil and smoke ?

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